Many existing security systems employ PIR sensors to detect a potential intruder. There is, however, a problem with security systems based upon the prior art, in that there is the potential for non-human “false alarm” triggers. Preventing false alarms and ensuring detection is of great importance to PIR motion detectors used in the security industry, as “false alarms” cause the stakeholders to lose confidence in the conventional alarm system as a reliable indicator of an intruder incursion leading to the conventional security system no longer being armed, making the security system mute.
In addition, PIR sensors in existing security systems are generally mounted internally and are part of an alarm system that is housed within the same building. These PIR sensors, when triggered, send an alert to the alarm control panel, which in turn activates the system's single strobe light. The intruder has already entered the property before any deterrent is initiated.
Conventional alarm system detectors are also generally placed internally, within a building, and these detectors often need to be hardwired and/or installed by a professional alarm system installer. Moreover, conventional alarm systems are often powered by the main electrical system of the structure in which they are located. They are thus vulnerable to power failures affecting the structure itself.
The prior art teaches various approaches to reducing the incidence of “false alarms” in alarm systems. For example in U.S. Pat. No. 4,614,938 to Weitman and U.S. Pat. No. 4,963,749 to McMaster disclose the use of a single quad PIR sensor having four IR sensitive elements, as well as two PIR sensor devices each having a pair of IR sensitive elements. The advantage of two channels over one is simply greater reliability of sensor output signal. An alarm signal is thus only generated when both channels indicate motion.
In U.S. Pat. No. 4,697,081 to Baker, a quad element sensor is disclosed in which interdigitated IR sensitive elements are provided. By this arrangement, both IR elements respond to infrared radiation collected by the lens, and the risk of false triggering is reduced. In U.S. Pat. No. 5,045,702 to Mulleer, a single channel detector is disclosed in which the sensor element configurations include a diamond pattern with opposed pairs of IR sensitive elements of opposite polarization connected in series. Such motion detectors typically employ a single lens to direct infrared radiation onto the single quad or multi-element sensor.
It is also known in the art to provide dual lens and dual sensor motion detectors. Such systems conventionally have a single housing with two lenses mounted one above the other. Each sensor receives radiation from one corresponding lens. The optical arrangement is such that infrared radiation from a person entering a detection zone will not be simultaneously received by both sensors, but rather sequentially. The response from the sensors is thus separated in time, and has a same polarity since the sensor IR sensitive elements of the two sensors are aligned parallel with like polarity. Such a dual channel motion detector can generate an alarm accurately when the response in both channels is similar and separated in time by the expected amount.
Thus, a need exists for a security system that provides security devices that may be installed on the exterior of a building or structure that not only efficiently prevents false alarms but also allows for communication with other similar security devices to create a community security alarm system.